In our previous study we demonstrated rat T cell factors having affinity for IgE. One of the IgE-binding factors has the ability to selectively enhance the IgE response (IgE-potentiating factor) and another factor selectively suppressed the IgE response (IgE-suppressive factor). In the next fiscal year, 1) we shall study the differences between the two factors with respect to their physicochemical properties and the source from which the factors are derived. 2) Mechanisms for the formation of IgE-suppressive factors will be studied using rat lymphocytes, 3) IgE-binding factors of similar biologic activities will be searched in the mouse as well.